Lubricating fluids are used in many technology fields like for instance in vehicles, energy producing equipment and metal working processes. Tribologically active additives have since many decades been developed in order to reduce the energy consumption and prolong the life-time of the lubricated surfaces. Most of the additives are organic or organometallic compounds with an ability to form protective tribological layers on the friction surfaces.
Lubricants in roller bearings and friction bearings ensure that a film of lubricant, which transfers loads and separates different parts, is established between parts that rub or slide against one another. This achieves the result that metallic surfaces do not come in contact with one another and therefore there is no wear. The lubricants must therefore meet high demands. These includes extreme operating conditions such as very high or very low rotational speeds, high temperatures caused by high rotational speeds or by long-distance heating, very low temperatures, e.g., in bearings that operate in a cold environment or which occur with use in aviation and space travel. Likewise, modern lubricants should be suitable for use under so-called clean room conditions in order to avoid soiling of the room due to abrasion and/or the consumption of lubricants. Furthermore, in use in modern lubricants, evaporation and thus “lackification,” i.e. such that they become solidified after a short application and no longer manifests a lubricating effect, should be avoided. Especially high demands are also made of lubricants during use such that the running surfaces of the bearings are not attacked due to slight friction, so that the bearing surfaces run noiselessly and long running times without relubrication are promoted. Lubricants must also withstand the action of forces such as centrifugal force, gravitational force and vibrations.
The improvement of wear and friction resistance of moving parts in bearings and machines is highly desirable in the modern automotive and transportation industry, as a major part of machine breakdowns are caused by mechanical wear of their moving parts. Typically, friction between moving parts in a system is reduced with different kinds of lubricants separating the moving parts, as lubricant-to-surface friction is much less detrimental than surface-to-surface friction.
Current market trends require lubricant and grease compositions having improved efficiency regarding friction, durability and wear.
Metal salts have been used for affecting the wear properties like for instance in U.S. Pat. No. 4,705,641 of Nov. 10, 1987 where an oil additive is presented which provides improved oxidation stability and anti-wear properties. The additive is based on a copper salt and a molybdenum salt in amounts ranging between 0.002 and 0.3 weight percent and 0.006 and 0.5 weight percent, respectively. The metal salts are selected from carboxylates like for instance naphthenates, oleates and stearates in order to make the metal more compatible with the oil. Similar compositions are disclosed in U.S. Pat. No. 4,431,553 and U.S. Pat. No. 4,552,677.
The abstract of CN 102174341 of Sep. 7, 2011 describes a method for preparing a stable nano-sized copper-based lubrication oil additive prepared by starting from a copper chloride—sodium hydroxide solution, which was filtered and further reacted with formic acid after which the formed Cu-formate powder was dried and milled. Part of the Cu-formate was immobilized on carbon-nanotubes and mixed together with the Cu-formate powder into lubrication oil whereby a stable dispersion was obtained. Furthermore, US 2012/101013 A1 discloses a lubricant composition comprising nanoparticles having an inorganic core and a block copolymer component. The inorganic core may comprise oxides, such as calcium oxide, magnesium oxide and metals, such as metallic aluminum, metallic tin.
In U.S. Pat. No. 6,613,721 of Sep. 2, 2003 a lubricant additive is disclosed. The additive is based on a colloidal suspension of single metal particle cores surrounded by surfactants. The size of colloids are in the range of 0.5-4 μm and contains one of the metals selected from bismuth, zinc, copper, tin or silver. The surrounding surfactant is selected from sarcosinates, sulfonates or octadecenyl amine.
WO 2012/107649 of Aug. 12, 2012 describes an optimized lubricant additive composition based on oil soluble metal salts of inorganic and organic acids in combination with standard oil additives. According to the disclosed compositions a thin friction reducing metal film is formed on the sliding surfaces. A similar composition is disclosed in RU2277579 of Jun. 10, 2006 where a composition based on metal salts and a mixture of standard lubrication additive components like for instance succinimide, aromatic amines, epoxy resins and aliphatic alcohols have been used as wear reducing additive in lubricants. Similar compositions are disclosed in RU 2311447 and RU 2338777. However, the lubricating composition has been found to suffer from poor stability due to poor compatibility of the components used.
The Russian patent RU 2,124,556 describes metal-plating compositions comprising a metal powder based primarily on copper having a particle size in the micrometer range. Preferably, the particles are produced by way of evaporation and a subsequent condensation in inert gas. It is claimed that this combination of components overcomes the problem of agglomeration and sedimentation as well as providing effective metal plating performance to protect against wear and reduce friction between metal surfaces. Similar compositions are described in Russian patent RU 2,503,713 for use as a grease additive. However, these lubricating compositions have been found to suffer from poor stability due to agglomeration and sedimentation of particles. Furthermore, the compositions have a low performance, especially in friction and wear.
Although this prior art shows that useful additive compositions are available it also shows that there are shortcomings. It is a critical requirement to improve the properties of the additive compositions and the lubricant and grease compositions in order to produce a stable and effective performance additive system. These important improvements are achieved in the present invention.